1. Field of the Invention
This invention relates to printer control systems and relates more particularly to such control systems for multi-velocity bidirectional printers in which the stopping distance of the print mechanism is controlled.
2. Description of the Prior Art
Some current bidirectional printers are controlled so that the print carriage can travel at one of a number of selected velocities for each line printed, depending upon the particular printing application being carried out. Such printers often are used in a closed loop servo system in which the command to stop is issued to the print mechanism drive prior to the time the print mechanism reaches the end of a line, in order to permit the system to decelerate the print mechanism at the proper point.
The distance traveled, once stopping is started, until zero velocity of the print mechanism is reached is dependent on the initial velocity. In such printers, the distance required to bring the print mechanism back up to the desired speed in the opposite direction after stopping is also determined by the velocity since the acceleration is constant. The difference in stopping distance (and also time) between the different speeds employed can cause a problem in some situations. For example, if a stop is done at low speed and the next start is to be at high speed, the distance traveled by the print mechanism into the margin at low speed is much less than the distance needed for the print mechanism to come up to the proper speed when leaving the margin at high speed. This would mean that the velocity when printing begins would be too slow and an error condition would result. Also, the time to go into and out of the margin at low speed would not be long enough to allow the paper forms on which printing is taking place to move and be in the proper position for printing of the next line.